System for vibrating industrial screens



Jan; 10, 1928. 1,65? ,482

c. s. WEYANDT SYSTEM FOR VIBRATING INDUSTRIAL SCREENS Filed Jan. 29, 1924 S iii 18 I L Emu! lmu j Patented Jan. 10, 1928.

UNITED STATES PATENT OFFICE.

CARL S. WEYANDT, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR T NATIONAL ELEC- TRIC MANUFACTURING COMPANY, A CORPORATION OF DELAWARE.

SYSTEM FOR VIBRATING INDUSTRIAL SCREENS.

Application filed. January 29, 1924. Serial No. 689,804.

v In the present. systems for controlling the vibration of industrial screens, a relatively large electromagnet provided with a springrestrained armature is so disposed that the armature vibrates the screen. The magnet 1 is energized by low frequency currents derived from special generators, whereby the spring is thus permitted to retract the armature from the energized position of the magnet as the current passes through the zero 2 values, or the magnet is energized through periodically operative switching devices.

When the electromagnet is energized from the usual or 60 cycle light and power circuit, the spring cannot become efiective to 25 retract the armature, since the magnet becomes energized at each alternation before the spring can actuate thearmature very far. The actual movement of the armature is hardly perceptible and is insuflicient to vibrate a screen, especially when it is loaded. If aswitching device or commutator be employed to control the periodic energize,-

tion of the electromagnet, the disadvantage of arcing between contact surfaces is introduced with the consequent requirements of' attention, replacement, adjustment, etc. Since industrial screens of diflt'erent kinds are required to shake relatively large loads, the electromagnet for vibrating the screen may require a relatively large energizing current. As the value of current, which the switch or commutator must break, increases, the arcing increases. For that reason current switching devices are unsatisfactory to control the vibrating magnet for the screens. In practicing my invention, I provide a stationary control valve or unidirectional current-conducting device, such as an electron valve or an electrolytic valve, in the circuit of the electromagnet to transmit energy impulses corresponding substantially to the current waves of one polarity from an alternating current circuit. During the rel atively long intervals between the impulses the electromagnet is de-energized or substantially de-energized, and the spring becomes eflective to retract the armature from its energized position. By properly disposing the armature in operative relation to the screen, the movements of the armature may be caused to effectively vibrate the screen. The disadvantages of switching devices and moving commutating devices are thereby obviated.

Fig. 1 of the accompanying drawings is a diagrammatic view of an electrical circuit illustrating the arrangement of the control elements of an industrial screen in accordance with the principle of my invention whereby the screen 'may be vibrated,

Fig. 2 is a front elevational view partially 1n section of a screen to be vibrated and the vibrating magnet therefor;

Fig. 3 is an oscillogram of the current waves supplied to the electromagnet in the circuit illustrated in Fig. 1;

Fig. 4 is a diagrammatic view of an electrical circuit in which an electrolytic valve is used; and

Fig. 5 is an oscillogram of the current supplied to the electromagnet through the electrolytic valve in Fi 4 As illustrated in Fig. 1 of the drawings,

the screen mechanism comprises, in general, a screen 10, an electromagnet 11 for vibrating the screen 1.0 and a control device, such as a vacuum valve 12 for controlling the energizationof the electromagnet to vibrate the screen.

As illustrated in Fig. 2. the screen 10 is supported between two side frames 13 and 14 and may be provided with suitable means 15, as illustrated in Fig. 1, to vary the tension on the screen to draw it taut. The side frames 13 and 14 are supported upon vertical supports 16 and 17 which in turn sup port a cross bracket or frame 18 which supports the electromagnet 11 above the screen. Suitable adjusting devices 19 are provided to adjust the. position of the electromagnet 11 and the cross-bracket 18, and thereby control the tension efi'ect of the electromag net on the screen.

The electromagnet 11 comprises a core member 20, and energizing coil 21 and a movable armature 22. A spring 23 is provided as illustrated in Fig. 1 to retract the armature 22 from the core when the coil is de-energized. The spring may not be necessary in many applications, since the Weight of the screen, loaded or unloaded, will suffice to retract the armature from the core during intervals when the electromagnet is de-energized. An adjustable back stop 24 may be provided to limit the extent of movement of the armature by the spring, and thereby control the-extent of movement of the screen.

In the structure which is illustrated in Fig. 2, the movement of the armature 22, attached to the screen 10 at 10", is controlled by two guides 25, and the base 26 of the housing enclosing the electromagnet serves as a back stop for the armature.

The movement of the screen is thus effected between limits determined by the distance between the armature and the core of the electromagnet, and by the position of the cross bracket 18 as determined by the adjust ing: devices 19.

he energization of the electromagnet 11 is so controlled by the vacuum valve 12 that the coil is periodically energized by impulses of current having intervals of zero current value there between.

During such intervals the operating coil is de-energized and the spring or the weight of the screen retracts the armature from energized position. The armature and, consequently, the screen are vibrated at a frequency depending upon the frequency of the impulses transmitted by the valve.

The valve 12 illustrated in Fig. 1 comprises an electron emitting body or cathode such as a filament 36 and an anode 27. The cathode is energized by means of a trans former 28 that derives its energy from an alternating current circuit 29.

' The electron valve 12 operates to transmit the complete current waves of one polarity and to suppress the complete waves of opposite polarity, as illustrated in Fig. 3. The intervals between the waves, or energy impulses, are of distinct and finite duration during which the electromagnet is de-energized and the armature retracted from en ga-gement with the core.

It will be observed from the oscillogram in Fig. 3 that the duration of the respective intervals between waves is less than the duration of the current waves. This characteristic, obtained by the combination of an asymmetric conductor and an inductive device such as electromagnet, introduces certain advantages in the present application. Since the screen is usually loaded, the increased interval of time provided for the operation of the electromagnet in raising the screen introduces smoother operation in vibrating the screen. The long interval occurs when work must be done to raise the (r 21, and of the general unit-29, and the impulse may persist, for example, for about three-fourths of a complete cycle, with a succeeding interval of zero current, before commencement of the next cycle, of a duration of about one-fourth of a cycle. There is but one impulse for each complete cycle of the impressed electro-motive-force,

whereby the magnet armature, and therefore 7 the screen and its load, are electro-magnetically actuated once per cycle of the supply circuit, and are restored, during periods of no current, once per cycle of the supply circuit.. These relations are of practical importance in the actuation or control of 'a screen or the like. The relatively long duration of the current impulse is of advantage in that for a given amplitude of movement of the loaded screen agreat electro-magnetic lifting force may be applied thereto, with ample time fully to accelerate the screen and.

its load before sudden stopping thereof. The substantial duration of the period of zero current, during which no electrical energy is consumed and the screen and its load return, is of practical advantage in that the screen and its load attain a high velocity which is suddenly reduced to zero, affording efiicient screening action. periods of zero current of substantial duration, the electro-magnet is more efficient, and a greater amplitude of vibration is obtainable, since during the period of zero current there is no electro-magnetic force resisting the return movement of the screen and its load. and there is no consumption of electrical energy during that period. In general, more efficient screening is obtainable, or at a given amplitude of vibration and with a given energy input a greater number of screen vibrations are obtainable in a unit of time. Furthermore, by this mode of screen operation, the character or quality of vibration is less affected by suddenly increasing the load of material upon the screen because of the substantial length of the periods of zero current. The utilization of current impulses separated by substantial periods of zero current avoids the necessity for special low frequency supply current. and permits efiective utilization of alternating current of commercial frequencies, as of 25 or cycles per second. The substantial periods of zero current are of advantage both in the matter of reduction of consumption of electric energy for a given amplitude of vibration of a given load, and because the screen and its load in their return movement loo Because of the are not electro-magnetically resisted, and the electrical energy otherwise expended during the return movement is'conserved.

Smooth operation of the screen is thus obtained by means of a stationary control device which does not embody contacts liable to troublesome arcing and therefore requiring attention.

A control system of the present character is particularly advantageous in view of the amount of dust present in the air near industrial screens. The present control equipment may be disposed near the screen to obviate the expense of conduit and cable which are necessary when arcing contactive devices are employed, since the latter must be disposed at a distance because of the dust in the surrounding air.

The advantages of non-arcing devices for applications of the character here considered cannot be over-emphasized. Arcing devices embodying movable contacts require practically constant service and attention.

In Fig. 4: is illustrated a modified control system, in which an electrolytic valve 30 is used to control the energization of the electromagnet. V

In Fig. 5 is an oscillogram of the current transmitted to the electromagnet through the electrolytic valve of Fig. 4.

It will be observed that the duration 01' the positive waves transmitted by the electrolytic valve 30 corresponded substantially to the duration of the waves transmitted by the vacuum valve 12 and the duration of the negative waves correspond substantially to the duration of the intervals of zero current value in the circuit of the vacuum valve. Thus, in so far as the operating interval is concerned, the same advantage of an operating interval of extended duration is obtained from either the vacuum or the elec-' trolytic valve. The small negative current wave transmitted by the electrolytic valve, however, serves to neutralize the residual magnetism remaining in the core of the electro-magnet, after being energized by the positive wave. Release of the armature is then readily permitted under the influence of the spring, or of the weight of the screen.

The small negative wave transmitted by the electrolytic valve is insuflicient to do more than neutralize the residual magnetism of the core. Practically, therefore, the electrolytic valve transmits preponderatingly unidirectional energy impulses that are substantially equivalent, in effect, to the im pulses transmitted by the vacuum valve.

By utilizing an asymmetric conductor, such as the vacuum or the electrolytic valve, or any other device that will transmit only prepouderatingly unidirectional energy 1mpulses from an alternating current, the expense of special apparatus is obviated. Moreover, the disadvantages incident to the operation of switching devices,-comprising contact members subject to arcing, are likewise avoideda.

My invention thus contemplates the em ployment of stationary, non-arcing, current controlling devices that will transmit preponderatingly unidirectional energy impulses, whereby the armature of an electromagnet may be vibrated in a predetermined desired manner.

Although my invention is illustrated herein as applied particularly to the operation of an industrial screen, it may just as well be applied to other applications in which the reciprocating movement of an armature may be utilized to do useful work, without departing from the spirit and scope of my invention as set forth in the appended claims.

\Vhat I claim is:

1. In the art of screening material by screen vibrations, the method ofvibrating the screen which comprises selecting from a source of alternating current by asymmetrical electrical conduction successive substantially spaced unidirectional current impulses, efi'eeting successive movements of the screen in the same direction by said current impulses, and efiecting successive return movements of the screen during the periods between said impulses.

2. In the art of screening material by screen vibrations, the method of vibrating the screen which comprises selecting from a source of alternating current by asymmetrical electrical conduction successive uni-directional current impulses spaced from each other by substantial periods shorter than their durations, eiiecting successive move ments of the screen in the same direction by said current impulses, and effecting successive return movements of the screen during the periods between said impulses;

3. Inthe art of screening material by screen vibrations, the method of vibrating the screen which comprises selecting from a source of alternating current by asymmetrical electrical conduction successive substantially spaced unidirectional current in1- pulses, eflecting successive movements of the screen in the same direction by said current impulses and simultaneously storing energy in a resilient system during each of said screen movements, and expending the stored energy in eilecting successive return movements of the screen during the periods between said impulses.

4. In the art of screening material by screen vibrations, the method of vibrating the screen which comprises selecting from a source of alternating current by asymmetrical electrical eonduction successive unidirectional currentimpulses spaced from each other by substantial periods of zero current, effecting successive movements of the screen'in the same direction by said current impulses and efiectin successive return movements oi the screen uring the periods of zero current.

5. In the art ofscreening material by screen vibrations, the method of vibrating the screen which comprises selecting from a source of alternating current by asymmetrical electrical conduction successive unidirectional current impulses spaced from each other by substantial periods of zero current shorter than their durations, effecting successive movements of the screen in the same direction by said current impulses, and efl'ecting successive return movements of the screen during the periods of zero current.

6. In the art of screening material by screen vibrations, the combination with a screen, of a magnet winding, a magnetizable member actuated thereby, a source of alternating current, and an electric valve in circuit with said source and said winding, whereby said screen is actuated by said magnetizable member under the influence of successive unidirectional current impulses traversing said valve and said winding.

7. In the art of screening material by screen Vibrations, the combination with a screen, ofa magnet winding, a magnetizable member actuated thereby, a source of alter-, nating current, an electric valve in circuit with said source and said winding, where by said screen is actuated by said magnetizable member successively in one direction under the influence of successive uni-directional current impulses traversing said valve and said winding, and a spring for returning said screen during thev intervals between said uni-directional impulses.

8. In the art of screening material by screen vibrations, the combination with a screen, of a magnet winding, a magnetizable member actuated thereby, a source of alternating current, and a thermionic valve in circuit with said source and said winding, whereb said screen is actuated by said magnetizab e member under the influence of successive uni-directional current impulses traversing said valve and said winding and spaced from each other by substantial periods of zero current.

9. 111 the art of screening material by screen vibrations, the combination with a screen, of a magnet winding, a magnetizable member actuated thereby, a source of alternating current, a thermionic valve in circuit with said source and said winding, whereby said screen is actuated by said magnetizable member successively in one direction under the influence of successive uni- 1 directional current impulses traversing said other by substantial periods of zero current,

11. In the art of screening material by screen vibrations, the combination with. a screen, of a magnet winding, a magnetizable member actuated thereby and attached to said screen, means for placing said screen under tension, a source of alternating current, an electric valve in circuit with said source and said winding, whereby said screen is actuated by said magnetizable member successively in one direction under the influence of successive uni-directional current impulses traversing said valve and said winding, and a spring for returning said screen during the intervals between said unidirectional impulses.

12. In the art of screening material by screen vibrations, the combination with a screen, of a magnet winding, a magnetizable member actuated thereby and attached to said screen, means for placing said screen under tension, a source of alternating current, and a thermionic valve in'circuit with said source and said winding, whereby said screen is actuated by said magnetizable member under the influence of successive unidirectional current impulses traversing said valve and said winding and spaced-from each rent, a thermionic valve in circuit with said source and stud wmdmg, whereby said screen I is actuated by said magnetizable member successlvely 1n one direction under the influence of successive uni-dlrectlonal current 1mpulses traversing said valve and said winding and spaced from each other by substantial periods of zero current, and a spring for returning said screen during said periods of zero current.

In testimony whereof, I have hereunto subscribed my name this 28th day of January CARL S. WEYANDT.

105 other by substantial periods of zero current. 

